In high intensity focused ultrasound (HIFU) an array of ultrasonic transducer elements are used to form an ultrasonic transducer. Supplying alternating current electrical power to the transducer elements causes them to generate ultrasonic waves. The ultrasonic waves from each of the transducer elements either add constructively or destructively at different locations in the beam path. By controlling the phase of alternating current electrical power supplied to each of the transducer elements the focal point or volume into which the ultrasound power is focused may be controlled.
High-intensity focused ultrasound (HIFU) therapy of tumors requires a high degree of spatial accuracy in order to avoid damaging healthy tissue as well as to obtain optimal usage of the system. Although avoiding damaging healthy tissue due to poor targeting is typically not a problem for large stationary tumors if utilizing low-power test sonications as is current practice, the technical performance and/or clinical performance of the system may suffer if incorrect positional knowledge is used for a feedback algorithm for example. This translates into reduced treatment efficiency.
The European patent application EP 0627 206 discloses an ultrasound medical treatment system which spatially resolves the hot spot and prevents displacement of the hot spot form the focal point of the ultrasound beam. The hot spot is resolved on the basis of an energy irradiation at a prescribed level lower than that of a treatment energy irradiation.